Vinyl acetate (VAC) is a kind of important organic chemical raw material which can generate such derivatives as polyvinyl alcohol (PVA), ethylene vinyl acetate copolymer (EVA), polyvinyl acetate (PVAC), and vinyl acetate-vinyl chloride copolymer (EVC) through self-polymerization or copolymerization with other monomer. These derivatives are widely used in many aspects, such as adhesive, adhesive agents in paper or fabric, paint, ink, leather processing, emulsifier, water soluble film, soil-improvement agent and so on. And there is a growing need of VAC as intermediates along with the extensive non-fiber applications field of polyvinyl alcohol.
The production of VAC began from the 1960s in China. After the “acetylene fluidized bed technology” was introduced from Japan by Beijing Organic Chemical Plant in 1965, multiple sets of similar devices were established in China. These VAC devices were established for the supporting of vinylon industry. And about 90% of the VAC were used for vinylon and PVA industry in China from the 1970s to the 1980s. The market of VAC has broadened with the development of PVA in China in recent years. By the end of 2008, the total production capacity of VAC reached 1,400,000 tons per year in China. And the demand for VAC is expected to grow at a rate of 8% in China in the future.
There are two processes for producing VAC, which are ethylene method and acetylene method. Ethylene method plays a dominant role in the world, while acetylene method is used only in a few countries such as China and almost abandoned in most of the foreign countries for the serious pollution of acetylene. The production process of VAC by ethylene method comprises: leading the raw material of ethylene, acetic acid and oxygen gas into a reactor, and contacting the raw material with the catalyst in the reactor to generate VAC, water and a small amount of by-products at the temperature of 130˜200° C. under the absolute pressure of 0.6-1.1 MPa; condensing the reactant gas at high temperature by multi-stage condensing to generate condensed solution containing VAC, water and unreacted acetic acid, etc. Then the solution of the mixture is sent to rectification stage for the refining of VAC. Non-reacted ethylene gas is returned to the compressor for recycling, known as cycling gas.
Ethylene is one of the world's highest output chemical products and also the most important basic chemical raw materials, which plays an important role in the national economy. Ethylene is one of the raw materials for the synthesis of VAC. In the production process of VAC by ethylene method, the single-way conversion rate of ethylene is only about 10%, and the large amount of unconverted ethylene have to be recycled. In order to prevent the accumulation of inert gas such as nitrogen, part of the refined gas mainly composed of ethylene has to be discharged thus causes the loss of ethylene. Selecting optimum absorbent solution and developing new processes to recover ethylene gas and reduce the emission of ethylene gas can lower the production cost of VAC and improve the market competitiveness of the products.